Blender Git Loki

UI DPI scaling:

Recoded the (2.65.1 version) region scale, which happened on loading files with
different saved size windows. Also scaling window itself was affected.

Old method: scaled region widths based on area/editor scaling factors.
That was leading to too small or too large button regions easily.

New method: region width/height now are in DPI control. Much nicer!
- On changing dpi, buttons remain visually same widths.
- On changing window sizes, the button views and zooms stick to exactly same.

Caveat: people who were using Blender with 'extreme' dpi setting, might find
the layouts slightly differ. Not sure if this is worth version patching...

Todo: overlapping regions that overlap together draw badly. Fix underway.